A saw chuck is used to hold a circular saw blade concentric with its centerline for grinding, tipping, swaging and gumming. The very early saw chucks were simply cone-shaped plugs going through the center or eye of the saw. This method of holding the saw is still widely used. One disadvantage in this method is that each time you remove the saw, you must first remove the cone. Another disadvantage of this cone-type centering device is that it offers no means of stabilizing the saw blade out away from the eye.
In the early 1970's the present inventor devised an improved method of chucking the saw for grinding. This commercially available saw chuck uses a solid steel plate with a shoulder machined on it for the eye of the saw. The plate has magnets imbedded in it to hold the saw plate flat and tight against the saw abutting face of the chuck. The use of the magnets tends to stabilize the saw and reduce vibration of the grinding wheel sharpening the saw. This method works well until the saw eye gets worn and no longer fits closely over the shoulder. When this occurs, the saw no longer is held concentric with the axis of rotation and therefore will not grind true.
In response to this, the present inventor came up with an improved magnetic saw chuck using a radially expanding segmented ring to center the eye of the saw on the chuck face. With this commercially available saw chuck, the segmented ring is made in three pieces and is held together with a steel spring clip. The segmented ring is mounted over a threaded arbor. A jam nut having a tapered forward face is tightened against the correspondingly tapered surfaces of the ring segments so that the ring segments expand against the saw eye to center the saw. Although this improved magnetic saw chuck is a marked improvement over the earlier saw chucks, moderate off-center chucking of the saw can still occur.